This invention relates to an optical pickup supporting device for use in an optical disc.
Generally, an optical pickup supporting device comprises a sheet metal base (chassis) having a generally plate-like shape, a main guide shaft mounted to the base in parallel to a plate surface of the base, and a sub guide shaft mounted to the base in parallel to both of the plate surface of the base and the main guide shaft.
When an optical pickup is driven by a drive mechanism, the optical pickup is guided by the main and the sub guide shafts in a tracking direction.
In order to meet various demands, such as a greater recording capacity of the optical disc and a higher access speed for the optical disc, it is required for an optical disc drive to have a high-accuracy mechanism. As one approach to achieve such a high-accuracy mechanism, it is proposed to improve the dimensional accuracy of components or parts of the optical disc drive. Practically, however, it is difficult to produce the parts of the optical disc drive with a higher dimensional accuracy than that achieved at present. Therefore, the above-mentioned approach can be carried out merely by producing the parts with the dimensional accuracy achieved at present and by selecting those parts which meet higher-accuracy criteria. In this event, the ratio of failed products, which are out of criteria and are not selected, is increased at the stage of parts production. This results in an increase in manufacturing cost of the optical disk drive.
In view of the above, attention is turned to another approach capable of realizing the high-accuracy mechanism without improving the dimensional accuracy of the parts. In this context, proposal is made of a method of adjusting mounting positions of the parts so as to allow dimensional inaccuracy to some extent.
As one of the parts mounting positions to be adjusted in the optical disc drive, there is an elevation angle position of each of the guide shafts for guiding the optical pickup used in the optical disc drive. The elevation angle position of the guide shaft is given by an elevation angle of the guide shaft, i.e., an angle in a vertical plane with respect to the plate surface of the base.
If the above-mentioned elevation angle position is not adjusted to an appropriate value, a laser beam emitted from the optical pickup cannot properly irradiate a data reproducing/recording surface of the optical disc. Specifically, an optical axis of the laser beam emitted from the optical pickup is inclined with respect to a principal surface of a disc table for supporting and rotating the optical disc. This phenomenon is called a skew error. Alternatively, the laser beam is not focused upon the data reproducing/recording surface of the optical disc.
In this connection, at least the main guide shaft is held and fixed on the base so that the elevation angle of the main guide shaft is adjustable by an elevation angle adjusting mechanism with respect to the plate surface of the base.
On the other hand, the sub guide shaft is not a driven part of the optical pickup which is driven by the drive mechanism but is a structure for guiding and supporting those parts following such driven part. Therefore, the sub guide shaft may not be provided with the above-mentioned elevation angle adjusting mechanism.
Next, description will be made about several existing optical pickup supporting devices.
A first existing optical pickup supporting device comprises main and sub guide shafts for guiding an optical pickup in cooperation with each other so that the optical pickup is moved in a predetermined direction. The sub guide shaft is made of resin and is attached to a sheet metal base by a so-called outsert molding.
A second existing optical pickup supporting device comprises a sheet metal base having first and second plate surfaces (upper and lower surfaces) and main and sub guide shafts arranged above the upper surface of the base for guiding an optical pickup in cooperation with each other so that the optical pickup is moved in a predetermined direction. Each of the main and the sub guide shafts is held and fixed on the upper surface of the base so that its elevation angle position (i.e., an elevation angle in a vertical plane along a thickness direction of the base) with respect to the upper surface of the base is adjustable. The optical pickup supporting device includes a pair of supporting units for supporting the main and the sub guide shafts, respectively. Each of the supporting units comprises a cylindrical cam member made of resin and rotatably attached to the upper surface of the base by outsert-molding, a holder made of resin and attached to the base to hold the main or the sub guide shaft, and a torsion spring attached to the base for pressing a peripheral surface of an end portion of the main or the sub guide shaft arranged above the base so that the guide shaft is urged towards the upper surface of the base. The cam member is provided with a spiral groove formed on its outer peripheral surface. The spiral groove receives the end portion of the main or the sub guide shaft. When the cam member is rotated, the end portion of the main or the sub guide shaft inserted in the spiral groove is moved upward or downward under the urging force of the torsion spring. Thus, the elevation angle position of the main or the sub guide shaft is adjusted.
A third existing optical pickup supporting device comprises a sheet metal base having first and second plate surfaces (upper and lower surfaces) and main and sub guide shafts arranged above the upper surface of the base. The main and the sub guide shafts serve to guide an optical pickup in cooperation with each other so that the optical pickup is moved in a predetermined direction. Each of the main and the sub guide shafts is held and fixed on the upper surface of the base so that its elevation angle position (i.e., an elevation angle in a vertical plane along a thickness direction of the base) with respect to the upper surface of the base is adjustable. The optical pickup supporting device comprises a pair of supporting units for supporting the main and the sub guide shafts, respectively. Each of the supporting units comprises a male screw engaged with a female thread portion formed in the base, a bent portion formed on the base for holding the main or the sub guide shaft, and a compression spring attached to the base for pressing a peripheral surface of an end portion of the main or the sub guide shaft arranged above the base so that the guide shaft is urged away from the upper surface of the base. The male screw has a flange portion formed at its end. The end portion of the guide shaft is held between the flange portion of the male screw and the compression spring. When the male screw is rotated, the end portion of the main or the sub guide shaft is moved upward or downward under the urging force of the compression spring. Thus, the elevation angle position of the main or the sub guide shaft is adjusted.
The first optical pickup supporting device has a metal part (the base) and a resin part (the sub guide shaft). Furthermore, the outsert molding is necessary to form the sub guide shaft on the base. Therefore, the number of steps is increased and the production cost is inevitably becomes high. In addition, it is relatively difficult to injection mold the sub guide shaft with high dimensional accuracy. Furthermore, because a major part of the sub guide shaft is arranged on the upper surface of the base, only a small space is left on the base to arrange other parts of the device. The above-mentioned structure is therefore disadvantageous in view of the reduction in thickness (height) of the optical disc drive.
The second existing optical pickup supporting device requires a large number of component parts and has a metal part (the base) and a resin part (the cam member). Furthermore, it is relatively difficult to injection mold the groove of the cam member with high dimensional accuracy. In addition, many component parts of the device are arranged on the upper surface of the base to occupy a relatively large space on the upper surface. This structure is therefore disadvantageous in view of the reduction in thickness (height) of the optical disc drive.
The third existing optical pickup supporting device also requires a large number of component parts. Furthermore, many component parts of the device are arranged on the upper surface of the base to occupy a relatively large space on the upper surface. This structure is therefore disadvantageous in view of the reduction in thickness of the optical disc drive.
In Japanese Patent Application No. 2001-16557, the present inventors have proposed an optical pickup supporting device which is simple in structure, small in occupation space on a base, and therefore advantageous in view of reduction in thickness of an optical disk drive.
The optical pickup supporting device mentioned above comprises a sheet metal base having first and second plate surfaces (upper and lower surfaces), and main and sub guide shafts both of which are made of metal. The main and the sub guide shafts serve to guide an optical pickup in cooperation with each other so that the optical pickup is moved in a predetermined direction. Each of the main and the sub guide shafts is held and fixed on the second plate surface of the base so that its elevation angle position (i.e., an elevation angle in a vertical plane along a thickness direction) with respect to the second plate surface of the base is adjustable. The optical pickup supporting device comprises a pair of supporting units for supporting the main and the sub guide shafts, respectively. Each of the supporting units comprises a male screw engaged with a female thread portion formed in the second plate surface of the base, and an extension spring directly or indirectly attached to a metal plate which is attached to the second plate surface of the base. The extension spring serves to pull an end portion of the guide shaft so that the guide shaft is urged away from the second plate surface. The male screw has a flange portion formed at its end. The end portion of the guide shaft is held by the flange portion of the male screw and the extension spring. When the male screw is rotated, the end portion of the guide shaft is moved upward or downward under the urging force of the compression spring. Thus, the elevation angle position of the guide shaft is adjusted.
The above-mentioned optical pickup supporting device has no resin parts and is therefore free from the problem of dimensional inaccuracy inevitable in molding of the resin parts. In addition, the number of component parts on the first plate surface of the base is relatively small. However, the number of component parts may possibly be reduced further.
Including the first through the third existing optical pickup supporting devices and the last-mentioned optical pickup supporting device, the device of the type generally has a comparatively large opening formed in the base to allow the movement of the optical pickup. Therefore, the sheet metal base may possibly be bent or warped. If the base is bent or warped, the flatness of the base is not kept and the guide shaft supported on the base is bent. This results in a skew error.
It is therefore an object of this invention to provide an optical pickup supporting device which is simple and compact in structure and requires a relatively small space, thereby contributing to reduction in thickness of an optical disc drive.
It is another object of this invention to provide an optical pickup supporting device which is capable of supporting an optical pickup with high accuracy.
The other objects of this invention will become clear as the description proceeds.
According to an aspect of this invention, there is provided an optical pickup supporting device for supporting an optical pickup and comprising a sheet metal base, a main track connected to the sheet metal base, and a sub track coupled to the main track, the main and the sub track guiding the optical pickup in cooperation with each other so that the optical pickup is movable in a predetermined direction above the sheet metal base, the sub track being formed by a part of the sheet metal base.